Spouse in extremis — case for narcotic? (8)
I believe the answer is:
sedative
'for narcotic?' is the definition.
(thesaurus)
'spouse in extremis case' is the wordplay.
'in extremis' says to hollow out the word (remove centre letters) (only the letters on the extremes are used).
'case' becomes 'dative' (the dative case in grammar).
'spouse' with its centre taken out is 'se'.
'se'+'dative'='SEDATIVE'
(Other definitions for sedative that I've seen before include "Tranquillising drug" , "Number" , "Sleep-inducing drug" , "Sleeping drug" , "Calming drug" .)